Apparatus for calculation of depth, trim, bending moment and shearing stress in a loaded ship



A nl 7, 1964 K. GRIMNES 5 APPARATUS FOR CALCULATION OF DEPTH, TRIM, BENDING MOMENT AND SHEARING STRESS IN A LOADED SHIP 3 Sheets-Sheet 1 Filed April 12, 1960 I ACTUAL WATER LINE F I G. 1 T

' 5 6 E 1 2 3 4 E 6 7 8 T PAINTED WATER LIN H f Y I F D INVENTOR KNUT' G-R/MNES ATTORNEY 5 Apnl 7, 1964 K. GRIMNES 3,128,375

APPARATUS FOR CALCULATION OF DEPTH, TRIM, BENDING MOMENT AND SHEARING STRESS IN A LOADED SHIP Filed April 12, 1960 3 Sheets-Sheet 2 eoa INVENTOR KNUT G-RIM/VES WWW,

ATTORNEYS 3,128,375 TRIM, BENDING SHIP April 7, 1964 K. GRIMNES APPARATUS FOR CALCULATION OF DEPTH MOMENT AND SHEARING STRESS IN A LOADED Filed April 12, 1960 5 Sheets-Sheet 3 INVENTOR KNUT G-RIM/VES WM {M ATTORNEYS United States Patent 3,128,375 APPARATUS FOR CALCULATION OF DEPTH, TRlh I, BENDlNG MOMENT AND HEAR1NG STRESES IN A LOADED SHIP Knut Grimnes, Trondheim, Norway, assignor to SINTEF, Trondheim, Norway Filed Apr. 12, 1960, Ser. No. 21,797 Claims priority, application Norway Apr. 28, 1959 12 Claims. (Cl. 235-479) This invention relates to apparatus for calculation of depth, trim, bending moment and shearing stress in a loaded ship.

The apparatus of the invention has been designed as an electric analog computer incorporating a number of sections (called apparatus sections) equivalent to a number of sections (called ships sections) into which it is assumed that the ship has been divided. The apparatus is based on the principle that in each apparatus section there can be obtained, by using fixed and adjustable resistors, a current (hereinafter called weight current) and a voltage (hereinafter called weight voltage), both being proportional to the arithmetic sum (hereinafter called resultant weight) of the buoyancy, carrying load and weight of the corresponding section of the ship.

In the accompanying drawings:

FIGURE 1 is a longitudinal section diagram of a ship divided into eight sections,

FIGURES 2 and 3 are circuit diagrams,

FIGURE 4 is a perspective view of an apparatus according to the invention,

FIGURE 5 is a wiring diagram of the apparatus, and

FIGURE 6 is a modified circuit diagram.

The basis for the design of the apparatus will be explained with reference to FIGURE 1, in which eight sections of a ship are designated 18. The depth of the ship midship is called D and the angle of trim T. The trim angle T is given in radians or, because it is generally very small, in tangents. An arbitrary section of the ship, will, in addition to the shearing stress and the bending moment acting in the sectional planes between the said section and adjacent sections be exposed to the following forces:

(i) The weight of the section, (ii) The load in the section, and (iii) The buoyancy of the section.

The weight of the section (i) is a constant for each section. The load in the section (ii) represents an arbitrary variable figure.

The buoyancy of the section (iii) is equal to the sum of two products, (a) the product of a constant buoyancy factor for each section and the depth midship, and (b) product of T, the distance from the section to midship and the buoyancy factor. The depth midship D is a variable common for all sections and independent of the load distribution. In the product (b), T is a variable, common for all sections, but depending upon the load distribution. The resultant weight F for each section is equal to the arithmetic sum of the weight of the section, its load and its buoyancy. When the ship is floating and in a static balance condition, the arithmetic sum of the resultant weights of all the sections of the ship equals 0. This can be expressed by the following equation:

This equation is valid, as will be understood, when divid ing the ship in eight sections such as shown in FIGURE 1.

3,128,375 Patented Apr. 7, 1964 8 ZF K O g=1 As the trim angle T is normally very small, the distance K varies with T and can be disregarded in Equation 2. The Equations 1 and 2 are according to the invention the basis for finding D and T respectively. In order to determine the bending moment M in an arbitrary intersection, for instance A in FIGURE 1, we use the following equation:

wherein x is positive towards the right hand side. In this equation, x, is the distance from the point of application of the resultant weight F, to the sectional plane A. Correspondingly, the following equation is used in order to determine the shearing stress S in the intersection between two sections 11 and n+1:

The principles for the design of an apparatus will now be described. As previously stated, there is obtained for each apparatus section, a weight current and a weight voltage both proportional to the resultant Weight of the particular ships section.

The load is an independent variable which is not influenced by the depth or the trim of the ship, and can therefore be represented by a current obtained either by using a constant voltage which can be common for every apparatus section and a variableresistor or by means of a fixed resistor and a variable voltage.

The weight of the ships sections is a constant figure and can be represented by a constant current, for instance obtained by using a voltage constant for every apparatus section and constant resistors one for each apparatus section.

By connecting these two resistors in a suitable way, a current equivalent to the sum of the weight and the load of the particular ships sections is obtained.

The buoyancy of the ships section can as previously explained, be regarded as the sum of the two products (a) and (b). The buoyancy of the ships section can therefore be represented by a sum of two currents. As the variable factors D and T are common for all apparatus sections, two variable voltages common for all apparatus sections can advantageously be used, each voltage being in combination with a resistor for each apparatus sections based upon buoyancy factor and the distance from midship of each corresponding ships section.

Such a Wiring scheme for apparatus section 1 is shown in FIGURE 2. Referring to this diagram, +e and e are constant voltages, e is a voltage which can be adjusted, for instance by using a potentiometer, so that it is proportional to D; this will be hereinafter explained. In a corresponding way, e is a voltage which can be adjusted so that it is proportional to T. All these voltages except 8T are common for all apparatus sections; e is of the same numerical value for each apparatus section, but is of opposite polarity for apparatus sections corresponding respectively forward of or aft midship.

P is a variable resistor adapted to be adjusted according to the load in the ships section. Likewise R is a constant resistor. The resistors P R and R are so adjusted in relation to each other and taking into account the characteristic data for the ships section in question, that the sum of the currents i and i (which are opposite due to the opposite polarity of the voltages +2 and e equals the weight of the section when the variable resistor is adjusted to maximum value (no load).

The resistors P (or P +R and R can theoretically be combined, but this has proved to be ineffective in practice.

R is given such a value that the current i corresponds to the products of D (voltage 2 and the buoyancy factor of the ships section. R is given such a value that the current 1' corresponds to the product of T (voltage o the buoyancy factor of the ships section and the distance of the section from midship. R is finally a constant resistor of a small value compared with the previously mentioned resistor. The current 1' as well as the voltage a over the resistor R will through this circuit be proportional to the resultant weight of the ships section.

It has been assumed hereinbefore that the voltages e and e are adjusted according to the value of D and T. It is obvious that if it is possible first to adjust these two voltages, values corresponding to D and T are obtained. It will now be explained how to obtain this adjustment.

From Equation 1, it follows that by a correct adjustment of e the sum of currents 1' 1' to iog will be 0. This will be the case substantially independent of T, i.e. substantially independent of e which can therefore be adjusted to an arbitrary value. Therefore, if the voltage a is adjusted, for instance by using a potentiometer until the sum of currents i 1' which can be read on a galvanomet'er, equals then the voltage ca is correctly adjusted and D can be read on the potentiometer.

In order to adjust e to its correct value, Equation 2 is used. When doing this, use is further made of the voltages e as shown in FIGURE 3. In this figure, R Rm designate constant resistors of such a value that its reciprocal value :(the conductivity) l/R for a certain apparatus section is proportional to the distance from the sectional plane in which one wants to calculate the bending moment to that particular ships section. The current:

is then proportional to the bending moment of the particular ships section in the sectional plane in question. The sum of all the currents equals then the total moment. If the apparatus is adjusted to the bending moment in one end of the ship or further out, it will be seen trom Equation 2 that the sum of the currents should be 0. In practice this is done by adjusting the voltage e by means of a potentiometer until the current i (which can be read on a galvanometer) equals 0. The potentiometer will then give the trim angle directly provided that the depth of the ship has been correctly set in beforehand. As previously explained the depth of the ship can be adjusted substantially independent of the trim angle. This is a permissible approximation.

The calculation of the bending moment and the shearing stress will be appreciated from the foregoing in connection with Equations 3 and 4.

When calculating the bending moment, there is calculated the moments for each ships section about the sectional plane for which it is desired to measure the bending moment. These moments are represented in the apparatus by currents I' These currents are obtained for all ships sections from the sectional plane to one end of the ship. The sum of these currents, z' is proportional to the bending moment in that particular sectional plane, see Equation 3. Similarly the shearing i stress in the sectional plane between ships section It and (n+1) is found by measuring the sum of the currents 1' to i This sum will be proportional to the shearing stress in the particular sectional plane, see Equation 4.

Like reference characters in FIGURES 1-5 designate corresponding quantities and parts.

FIGURE 5 shows the wiring for a calculating apparatus for a ship split into eight sections and where the shearing stress can be measured in two sectional planes and the bending moment in two sectional planes.

The apparatus includes a series of resistors (R) and potentiometers or adjustable resistors (P), two switches (S and M) and two galvanometers (A).

FIG. 5 is split into three areas, as indicated with dot and dash lines, one for a weight unit (area B, C, D, B), one for a moment unit (area C, D, F, G) and one for a control unit (area H, B, G, K).

To the left of the weight unit are five wires 11-15 each with its own voltage as indicated on the top of FIG. 5 +e and -2 are constant voltages, they are given relatively to a common zero point (=e in the control unit (see hereinafter) and they are of the same numerical value, but have opposite polarity. e is a voltage which is proportional to the adjusted depth of the ship. 6 and -e are voltages of the same numerical value, but opposite polarity and the value of the voltage is proportional to the trim angle (the angle between the painted water line of the ship and the real meter line along the ship). For each ships section there is a set of resistors, three of which, viz. for the sections 1, 2 and 8 are shown completely, while the other five are merely indicated symbolically with a resistor R -R All the resistors are indexed by two figures, the first figure indicating the location of the resistor in the set, while the second figure indicates to which set (section) the resistor belongs. With regard to the aim of the different resistors in each set reference is made to the previous description of FIG. 2, showing the first set of resistors at the top of FIG. 5. There is a small difference between the first resistor set and the following ones. The adjustable resistor in the first set of resistors is shown as a single adjustable resistor P If there is more than one tank in a ships section, for instance three, there is preferably provided one adjustable resistor for each tank, for instance (P P P and it is the parallel resistance of these resistors which equals P in FIGURE 2.

In the area for weight unit in the diagram there is a switch S working with 4 contacts a, b, c, and d. Contact a is permanently connected with the outputs from the resistors R and R contact 12 with the outputs from resistors R R and contact 0 with the out puts from resistors R and R Contact d is connected with the slider on a potentiometer P through which contact d can be supplied with an adjustable current (voltage). In the wiring diagrams the switch S is shown in the depth position, i.e., contacts a, b, c are short circuited. This means that all the lower ends of the resistors R are connected and the depth can be calculated as previously described in connection with FIGURES 1-3. If the switch is moved one step anti-clockwise, a is disconnected, while b, c and d are connected. If the current to contact d is adjusted so that the instrument A shows the same as in the depth position (which should be 0 when the depth is correctly adjusted) then the current to d is equal to the current which was disconnected through a, and it is therefore proportional to the shearing stress in the sectional plane between sec tions 2 and 3. In the next position the shearing stress in the sectional plane between *6 and 7 is measured in the same way. Shearing stress is read on the potentiometer P The moment unit includes a switch M with nine poles M M and a number of resistors.

The resistors R R R are used by calculating the trim, as described above in connection with FIGURE 3. Each of these resistors is of such a value that the conductivity (l/R of the resistors is proportional to the distance from one end of the ship to the section designated with the ciper of the resistor. In FIGURE 5, the switch M is adjusted to measurement of trim. The pole M is disconnected in this position.

In order to measure the bending moment in sectional plane A (FIGURE 1) resistors R R R and R are provided. These resistors are connected if the switch is moved one step clockwise. Then only resistors for the sections between sectional plane A and one end of the ship are connected and the current through instrument A will be proportional to the bending moment in the sectional plane A. In the embodiment shown the bending moment will not be read on the instrument A but on the potentiometer P by means of which a current is applied through the pole M which current can be adjusted so that instrument A shows 0. The current applied will then be of numerical value, but of opposite polarity to that which could be read on A and is therefore proportional to the bending moment in the sectional plane in question.

If the switch M is moved one step further, the resistors R R and R are connected corresponding to the measurement of bending moment in sectional plane B (FIGURE 1). It is understood that the resistors R and R have such values that the conductivity of a resistor (for instance R is proportional to the distance from the section (in the example section 7) indicated by the cipher index of the resistor to the sectional plane indicated by the letter index (in the example sectional plane A).

If the switch is turned all the way to the left (anticlockwise), then the moment unit is completely disconnected. This is done when one calculates the shearing stresses.

The control unit consists of a voltage divider R --R which is connected to two leads 11 and 12 and four potentiometers P P P and P the position of which gives respectively depth, trim, shearing stress and bending moment.

The voltage divider consists of two equal resistors R and gives a voltage 2 which is the zero point for the voltages in the apparatus. This makes the voltages +e and e numericaly equal, but of opposite polarity. This is of course only absolutely true as long as there is no current in the lead from the middle point of the voltage divider. Inasmuch as all the measurements are made in such a way that both A and A shall show 0 (or very close to 0), there should be no current in this lead when measuring and that s is therefore really half way between +e and e (or in any case within certain limits of tolerance). The potentiometer for depth: P is connected in series with a constant resistor R of such a size that e can be controlled between 0 and e e =0 given depth where buoyancy is 0, and as all sets of resistors are supplied with the same voltage 2 all the sections must have a buoyancy=0 at the same depth. If this is in fact not the case, the buoyancy curves and the weights of the sections must be adjusted. This is done by adjusting the buoyancy curve until its shows 0 buoyancy at the prede termined depth, whereafter the weight of the particular section is corrected, so that the sum of corrected buoyancy and corrected own weight equals the sum of buoyancy and weight of section before the correction was done.

The potentiometer P -P for trim is a double potentiometer, from which one obtains the two voltages e and e which are numerically equal, but of opposite polarity. One voltage is used for all the sections abaft midship, and the other for all sections forward of midship.

Potentiometers P for shearing stress and P for bending moment supply a current, the value of which depends upon the adjustment. This is possible because they are adjusted until instruments A or A show 0 (respectively for: shearing stress and bending moment). The voltagedrop over the respective amperemeter is then 0 and the voltage on the slider of the potentiometer equals e (:0).

There is therefore a relationship between the position of the slider and the current from the slider. The current will of course be proportional to the supply current, but so also will be current which the operator is trying to equal, and the result is that the position of the potentiometers indicates shearing stress and bending moment, independent upon the supply voltage. The circuit is in fact a bridge circuit, but it is easier to regard it as hereinbefore shown, because the analogy between the electrical and mechanical values is more apparent.

In the apparatus hereinbefore described and shown in the drawings, especially FIGURES 2 and 5, a variable resistor is provided for each apparatus section (for instance P for the first section), the said resistor being adapted to be adjusted corresponding to a load to be carried in the corresponding section of the ship. It is provided with a constant resistor (for instance R in series with the variable resistor. These resistors are connected to a constant potential (for instance +2 For the same section of the apparatus there is further provided a constant resistor (for instance R the value of which is selected corresponding to the own weight of the corresponding section of the ship. This resistor is connected to a constant potential (for instance e being of opposite polarity, but of the same numerical value as the constant potential (+e mentioned above.

These resistors R and R are so dimensioned that the arithmetical sum of the currents (i and 1' respectively) being obtained through resistors (R or R respectively) corresponds to the weight of the section of the ship when the variable resistor P is set to maximal value.

In practice the maximum carrying load (represented by i max.) will usually be substantially greater than the weight of the section of the ship (represented by i min. i For practical reasons it is not desirable to let the relation in min. i max.

be smaller than about /2, and 1' (determined by the value of R will therefore have a value close to the value of i min. (determined by the value of R In order to obtain the desired accuracy of the arithmetical sum of the two currents rather high requirements is made to the accuracy of each of the two resistors R and R FIGURE 6 shows a modification of the coupling here:

inbefore described, by means of which modification the difiiculty described is eliminated. In FIGURE 6, F designates a potentiomenter one end of which is connected to a point having a constant voltage +e and the other end is connected to zero potential. By means of the potentiometer, the voltage 2 can be adiusted on any value from O to +e The voltage e is applied across a resistor R and a current i' is obtained which can be adjusted from zero to a maximum value corresponding to the weight of the carrying load in the corresponding section of the ship.

R' is a constant resistor of such a value that the current 1". will correspond to the own weight of the section of the ship. Whereas the resistor R according to FIG- URES 2 and 5 is connected to the voltage e is the resistor R' according to FIGURE 6 connected to the plus pole of the apparatus, that is the voltage +2 In other respects the coupling is the same as shown in FIG- URES 2 and 5, and the designations e e R 1, R i 1' e i and R on the drawing designate corresponding voltages resistance and currents as the same designations in the other figures.

representing signal, a second signal-generating means adjustable to produce an electric signal in accordance with the adjustment so made to be used in the apparatus as a trim-representing signal, a plurality of elementary com puting means, one for each of a corresponding plurality of sections into which the ship is assumed to be divided, each elementary computing means comprising a Weightsignal-generating circuit and a buoyancy-force-signalgenerating circuit, the weight-signal-generating circuit including manually adjustable means settable in accordance with an associated scale means representing weight and operative to control the output of the first signal-generating circuit to provide an output current proportional to the sum of the weight of the corresponding section and the proposed load to be placed in it as indicated on the scale means, and the buoyancy-force-signal-generating circuit having first and second input channels and being operative to produce an output signal that is the sum of a first component output signal that is proportional to a first input signal applied to the first input channel with a gain representative of a predetermined buoyancy factor for the corresponding section and of a second component output signal that is proportional to a second input signal applied to the second input channel with a gain representative of the product of the buoyancy factor of the corresponding section and the distance of the section from a first reference transverse plane of the ship, the first and second input channels being respectively connected to receive the draught-representing and trim-representing signals as inputs, whereby the total output signal of the buoyancy-force-signal-generating circuit is representative of the buoyancy force that would be exerted on the corresponding section for the proposed manner of loading if the ship Were to have the values of draught and trim provided by the draughtrepresenting signal and trim-representing signal generating means, elementary summing means connected to receive the outputs of the weight-signal-generating circuit and the buoyancy-force-signal-generating circuit as inputs and to provide an output signal that is representative in magnitude and sense of their algebraic sum, and a moment-computing circuit operative to produce an out put signal that is proportional to an input signal with an adjustable gain, said computer apparatus also including first and second primary summing means, first and second switch means, said first switch means being selectively operable to connect the output signals of all the elementary summing means to the first primary summing means, and said second switch means being selectively operable to connect all the output signals of the elementary summing means as input signals to the corresponding moment-computing circuits, simultaneously to adjust the gains of the moment-computing circuits so as to make the gains respectively proportional to the distances of the corresponding sections from a second reference transverse plane, and to connect the output signals of all the moment-computing circuits to said second primary summing means, whereby, by suitable adjustment of the draught-representingsignal-generating means the trim-representing-signal-generating means to make the outputs of the first and second primary summing means substantially zero, more accurate values of draught-representing and trim-representing signals are obtained, said second switch means being further selectively operable to connect the output signals of the elementary summing means of those elementary computing means corresponding to those sections to one side of the first predetermined plane at which it is desired to calculate bending moment as input signals to corresponding moment-computing circuits, simultaneously to adjust the gains of the said moment-computing circuits so as to make the gains respectively proportional to the distances of the corresponding sections from the said first predetermined transverse plane, and to connect the output signals of the selected moment-computing circuits to the 8 second summing means to provide a measure of the bending moment.

2. An electrical analog computing apparatus for a ship for calculating the draught, the trim in the pitch plane, and the bending moment at a first predetermined transverse plane for a proposed manner of loading, comprising a first potentiometer means adjustable to produce a voltage in accordance with the adjustment so made to be used in the apparatus as a draught-representing voltage, a second potentiometer means adjustable to produce a voltage in accordance with the adjustment so made to be used in the apparatus as a trim-representing voltage, a plurality of elementary computing means, one for each of a corresponding plurality of sections into which the ship is assumed to be divided, each elementary computing means comprising a weight-signal generating circuit and a buoyancy-force-signal-generating circuit, the weightsignal-generating circuit including manually settable means settable in accordance with an associated scale means representing weight and being operative to control the output of the weight-signal-generating circuit to provide an output current proportional to the sum of the weight of the corresponding section and the proposed load to be placed in it as indicated on the scale means, and the buoyancy-force-signal-generating circuit comprising a first resistance having a fixed value corresponding to a predetermined buoyancy factor for the corresponding section and connected to the first potentiometer means to be energized by the draught-representing voltage, a secand resistance having a fixed value corresponding to the product of the buoyancy factor for the section and the distance of the section from a first reference transverse plane, and connected to the second potentiometer means to be energized by the trim-representing voltage, a third resistance having a fixed value low compared with the values of the other resistances and connected to receive the output current of the weight-signal-generating circuit and the currents through the first and second resistances in parallel, whereby the current through the third resistance and the voltage across it both represent the algebraic sum of the weight of the corresponding section, the load to be placed in the section as indicated on the scale means, and the buoyancy force on the section, a fourth resistance having a fixed value inversely proportional to the distance of the corresponding section from a second reference transverse plane, and each of those elementary computing means representing sections to one side of the first predetermined transverse plane having a fifth resistance having a fixed value inversely proportional to the distance of the corresponding section from the first predetermined transverse plane, said computer apparatus also including first and second current-summing means each operable to add algebraically currents supplied to it and to provide an indicated measure of the sum, first and second switch means, said first switch means being selectively operable to connect the currents through all the third resistances to the first summing means to provide an indicated measure of the algebraic sum of the currents and said second switch means being also selectively operable to connect the voltages across all the third resistances to energize respectively the corresponding fourth resistances and simultaneously to connect the currents through all the fourth resistances to the second summing means to provide an indicated measure of the algebraic sum of the currents, whereby, by suitable adjustment of the first and second potentiometer means, more accurate draughtrepresenting and trim-representing voltages are obtained, and said second switch means being further selectively operable to connect the voltages across the third resistances in those elementary computing means corresponding to those sections to one side of the predetermined transverse plane the bending moment at which is to be calculated, to energize the corresponding fifth resistances and simultaneously to connect the currents through the fifth resistances to the second current-summing means to provide an indicated measure of the algebraic sum of the currents and thereby of the bending moment at the predetermined transverse plane if the first and second po tentiometer means have been adjusted to produce accurate draught-representing and trim-representing voltages.

3. Apparatus as claimed in claim 2 wherein, in respect of those elementary computing means corresponding to those sections having more than one compartment, each manually settable means includes a plurality of settable knobs, one for each compartment, and each having a scale representing weight.

4. Apparatus as claimed in claim 2 including potentiometer means settable by means of a knob having a scale representing bending moment to produce a voltage corresponding to the setting so made, said second switch means being efiective to connect the output of the potentiometer means to produce a current in the second summing means when the latter is connected to receive the currents through the fifth resistances, whereby if the knob is adjusted to cause the second summing means to indicate zero, the knob indicates with respect to the scale the bending moment at the predetermined plane.

5. Apparatus as claimed in claim 2 for calculating the ending moment at a plurality of predetermined transverse planes, wherein the number of said fifth resistances correspond to the number of predetermined transverse planes to one side of the corresponding sections, and each having a fixed value inversely proportional to the distance of the corresponding section from the corresponding transverse plane, said second switch means being selectively operable to connect the voltages across the third resistances of those elementary computing means corresponding to those sections to one side of a selected one of the predetermined transverse planes to energize respectively those fifth resistances having fixed values inversely proportional to the distances of the sections from the selected transverse plane, and simultaneously to connect the currents through the selected fifth resistances to the second current-summing means to provide an indicated measures of the algebraic sum of the currents.

6. An electrical analog computing apparatus for a ship for calculating the draught, the trim in the pitch plane, the bending moment at a predetermined transverse plane, and the shear force at a predetermined transverse plane, for a proposed manner of loading, comprising a first potentiometer means adjustable to produce a voltage in accordance with the adjustment so made to be used in the apparatus as a draught-representing voltage, a second potentiometer means adjustable to produce a voltage in accordance with the adjustment so made, to be used in the apparatus as a trim-representing voltage, a plurality of elementary computing means, one for each of a corresponding plurality of sections into which the ship is assumed to be divided, each elementary computing means comprising a weight-signal-generating circuit and a buoyancy-force-signal-generating circuit, the weight-signal generating circuit including manually settable means settable in accordance with an associated scale means rep resenting weight and being operative to control the output of the weight-signal-generating circuit to provide an output current proportional to the sum of the weight of the corresponding section and the proposed load to be placed in it as indicated on the scale means, and the buoyance-force-signal-generating circuit comprising a first resistance having a fixed value corresponding to the predetermined buoyancy factor of the corresponding section and connected to the first potentiometer means to be energized by the draught-representing voltage, a second resistance having a fixed value corresponding to the product of the buoyancy factor for the section and the distance of the section from a first transverse plane and connected to the second potentiometer means to be energized by the trim-representing voltage, a third resistance having a fixed value low compared with the values of the other resistances and connected to receive the output current of the weight-signal-generating circuit and the currents through the first and second resistances in parallel whereby the current through the third resistance and the voltage across it both represent the algebraic sum of the weight of the corresponding section, the load to be placed in the section as indicated on the scale means, and the buoyancy force on the section, and a fourth resistance having a fixed value inversely proportional to the distance of the corresponding section from a second reference transverse plane, and each of those elementary computing means representing sections to one side of the first predetermined transverse plane having a fifth resistance having a fixed value inversely proportional to the distance of the corresponding section from the first predetermined transverse plane, said computer apparatus also including first and second current-summing means each operable to add algebraically currents supplied to it and to provide an indicated measure of the sum, first and second switch means, said first switch means being selectively operable to connect the currents through all the third resistances to the first summing means to provide an indicated measure of the algebraic sum of the currents and said second switch means being also selectively operable to connect the voltages across all the third resistances to energize respectively the corresponding fourth resistances and simultaneously to connect the currents through all the fourth resistances to the second summing means to provide an indicated measure of the algebraic sum of the currents, whereby, by suitable adjustment of the first and second potentiometer means, more accurate mean draughtrepresenting and trim-representing voltages are obtained, said second switch means being further selectively operable to connect the voltages across the third resistances in those elementary computing means corresponding to those sections to one side of the predetermined transverse plane the bending moment at which is to be calculated, to energize the corresponding fifth resistances and simultaneously to connect the currents through the fifth resistances to the second current-summing means to provide an indicated measure of the algebraic sum of the currents, and thereby of the bending moment at the predetermined transverse plane if the first and second potentiometer means have been adjusted to produce accurate draught-representing and trim-representing voltages, and said first switch means being further selectively operable to connect the currents through the third resistances of those elementary computing means corresponding to those sections to one side of the predetermined transverse plane the shear force at which is to be calculated, to the first summing means to provide an indicated measure of the algebraic sum of the currents and thereby of the shear force at the predetermined transverse plane if the first and second potentiometer means have been adjusted to produce accurate draught-representing and trim-representing voltages.

7. Apparatus as claimed in claim 6 wherein, in respect of those elementary computing means corresponding to those sections having more than one compartment, each manually settable means includes a plurality of settable knobs, one for each compartment, and each having a scale representing weight.

8. Apparatus as claimed in claim 6 including a third potentiometer means settable by means of a knob having a scale representing bending moment to produce a voltage corresponding to the setting so made, said second switch means being effective to connect the output of the third potentiometer means to produce a current in the second summing means when the latter is connected to receive the currents through the fifth resistances, whereby, if the knob is adjusted to cause the summing means to indicate zero, the knob indicates with respect to the scale the bending moment at the predetermined plane, and a fourth potentiometer means settable by means of a knob having a scale representing shear force to produce a voltage corresponding to the setting so made, said first switch means being effective to connect the output of the fourth potentiometer means to produce a current in the first summing means when the latter is connected to receive the currents through the third resistances of those elementary computing means corresponding to those sections to one side of the transverse plane the bending moment at which is to be computed, whereby if the knob is adjusted to cause the first summing means to indicate zero, the knob indicates with respect to the scale the bending moment at the predetermined plane.

9. Apparatus as claimed in claim 6 for calculating the bending moment at a plurality of predetermined transverse planes, wherein the number of said fifth resistances correspond to the number of predetermined transverse planes to one side of the corresponding sections, and each having a fixed value inversely proportional to the distance of the corresponding section from the corresponding transverse plane, said second switch means being selectively operable to connect the voltages across the third resistances of those elementary computing means corresponding to those sections to one side of a selected one of the predetermined transverse planes to energize respectively those fifth resistances having fixed values inversely proportional to the distances of the sections from the selected transverse plane, and simultaneously to connect the currents through the selected fifth resistances to the second current-summing means to provide an indicated measure of the algebraic sum of the currents, and for also calculating the shear force at a plurality of predetermined transverse planes wherein said first switch means is selectively operable to connect the currents through the third resistances of those elementary computing means corresponding to those sections to one side of any selected one of the transverse planes the shearing force at which is to be calculated to the first summing means to provide an indicated measure of the algebraic sum of the currents.

10. in an analog computer apparatus for a ship for calculating the bending moment at a selected trnasverse plane for a proposed manner of loading of the ship and having means to provide measures of the draught and trim of the ship for the proposed manner of loading, an elementary computing means, one for each of a plurality of sections into which the ship is assumed to be divided for computing a measure of the algebraic sum of measures of the weight of the corresponding section, the load to be placed in the section, and the buoyancy force that should act on the section for the proposed manner of loading, comprising means operable to produce a current having two components, one of constant magnitude representing the weight of the section and the other of variable magnitude representing the weight of the load to be placed in the section, adjustable means for varying the magnitude of the second component in accordance with the load to be placed in the section, means operable to produce a current representing the product of the measure of the draught of the ship and a factor dependent on the buoyancy characteristics of the section, means operable to provide a current representing the product of the measure of the trim of the ship, the said factor and the distance of the section from a reference transverse plane, and means to provide a measure of the algebraic sum of the currents.

11. An electrical analog computer apparatus for a ship for calculating the draught, the trim, and the bending moment at a predetermined transverse plane that the ship should have for a proposed manner of loading, comprising a first settable signal-generating means settable in association with a scale representing draught to produce an electrical signal representative of the value of draught indicated by the scale, a second settable signal-generating means settable in association with a scale representing trim to produce an electrical signal representative of the value of trim indicated by the scale, a plurality of elementary computing means, one for each of a correspondmg plurality of sections into which the ship is assumed to be divided, each elementary computing means comprising an elementary unbalance-force computing circuit having at least one electrical component adjustable in accordance with the weight of loads to be placed in the corresponding section and electrical components having fixed values predetermined in dependence upon the weight of the section, the buoyancy characteristics of the section and the distance of the section from a reference transverse plane of the ship and being connected to the first and second signal-generating means to receive the draught-representing and trim-representing signals so as to produce an electrical signal output that is representative of the unbalance force on the section if the ship, loaded in the proposed manner, were held with a draught and a trim corresponding to the values produced by the first and second signal-generating means, and an elementary moment-computing circuit having an electrical component having a fixed value predetermined in dependence on the distance of the corresponding section from a reference transverse plane, and arranged to produce an output signal that is a measure of the product of an input electrical signal and a factor representing the said distance, and each of the elementary computing means corresponding to sections to one side of the predetermined transverse plane, the bending moment at which is to be computed, having an elementary moment-computing circuit having an electrical component having a fixed value predetermined in dependence on the distance of the corresponding section from the predetermined transverse plane, and arranged to produce an output signal that is a measure of the product of an input electrical signal and a factor representing the said distance, said apparatus also including first and second summing means, first and second switch means, said first switch means being selectively operable to connect said first summing means to receive the electrical signal outputs of all the unbalance force-computing circuits to provide a measure of their sum and being selectively operable to connect all the electrical signals representing unbalance forces as input signals to corresponding ones of the first elementary moment-computing circuits and to connect the first summing means to receive the electrical signal outputs of all the first moment-computing circuits to provide a measure of the sum of the signals, whereby, by suitable adjustment of the first and second signal-generating means to make both the sum measures substantially zero, more accurate values of draught-representing and trimrepresenting signals are obtained, and said second switch means being also selectively operable to connect the electrical signals representing unbalance forces of those sections to one side of the predetermined transverse plane as input signals to corresponding ones of the second moment-computing circuits and to connect the second summing means to receive the electrical signal outputs of all the second elementary moment-computing circuits to provide a measure of the sum of the signlas and thereby of the bending moment at the predetermined transverse plane when the first and second signal-generating means have been adjusted to produce accurate values of draught and trim.

12. In an electrical analog computer apparatus for a ship for calculating the bending moment at a predetermined transverse plane and the shear force at a predetermined transverse plane for a proposed manner of loading, elementary computing means for each of a plurality of sections into which the ship is assumed to be divided for the purpose of the calculation, to produce a current and a voltage both of which represent the resultant force that should act on the corresponding section for the proposed manner of loading, a moment-computing circuit for each of those sections to one side of the plane the bending moment at which is to be calculated having a resistance having a value inversely proportional to the distance of the corresponding section from the plane, means to apply the voltages representing the resultant forces on those sections to one side of the plane to energise, respectively, the corresponding moment-computing circuits to produce currents through their resistances representing, respectively, the moments of those sections about a transverse axis in the plane, means for adding the currents to provide a measure of bending moment at the said plane, and means for adding the currents representing the resultant forces on those sections to one side of the transverse plane the shear force at which is to be calculated to provide a measure of shear force at the said plane.

References Cited in the file of this patent UNITED STATES PATENTS Hedin July 20, 1937 Muskat Mar. 10, 1953 Kolisch Nov. 29, 1955 Kolisch et al. Oct. 14, 1958 Swenson Dec. 23, 1958 Kolisch June 6, 1961 

1. AN ELECTRICAL ANALOG COMPUTING APPARATUS FOR A SHIP FOR CALCULATING THE DRAUGHT, THE TRIM IN THE PITCH PLANE, AND THE BENDING MOMENT AT A FIRST PREDETERMINED TRANSVERSE PLANE, FOR A PROPOSED MANNER OF LOADING, COMPRISING A FIRST SIGNAL-GENERATING MEANS ADJUSTABLE TO PRODUCE AN ELECTRIC SIGNAL IN ACCORDANCE WITH THE ADJUSTMENT SO MADE TO BE USED IN THE APPARATUS AS A DRAUGHTREPRESENTING SIGNAL, A SECOND SIGNAL-GENERATING MEANS ADJUSTABLE TO PRODUCE AN ELECTRIC SIGNAL IN ACCORDANCE WITH THE ADJUSTMENT SO MADE TO BE USED IN THE APPARATUS AS A TRIM-REPRESENTING SIGNAL, A PLURALITY OF ELEMENTARY COMPUTING MEANS, ONE FOR EACH OF A CORRESPONDING PLURALITY OF SECTIONS INTO WHICH THE SHIP IS ASSUMED TO BE DIVIDED, EACH ELEMENTARY COMPUTING MEANS COMPRISING A WEIGHTSIGNAL-GENERATING CIRCUIT AND A BUOYANCY-FORCE-SIGNALGENERATING CIRCUIT, THE WEIGHT-SIGNAL-GENERATING CIRCUIT INCLUDING MANUALLY ADJUSTABLE MEANS SETTABLE IN ACCORDANCE WITH AN ASSOCIATED SCALE MEANS REPRESENTING WEIGHT AND OPERATIVE TO CONTROL THE OUTPUT OF THE FIRST SIGNAL-GENERATING CIRCUIT TO PROVIDE AN OUTPUT CURRENT PROPORTIONAL TO THE SUM OF THE WEIGHT OF THE CORRESPONDING SECTION AND THE PROPOSED LOAD TO BE PLACED IN IT AS INDICATED ON THE SCALE MEANS, AND THE BUOYANCY-FORCE-SIGNAL-GENERATING CIRCUIT HAVING FIRST AND SECOND INPUT CHANNELS AND BEING OPERATIVE TO PRODUCE AN OUTPUT SIGNAL THAT IS THE SUM OF A FIRST COMPONENT OUTPUT SIGNAL THAT IS PROPORTIONAL TO A FIRST INPUT SIGNAL APPLIED TO THE FIRST INPUT CHANNEL WITH A GAIN REPRESENTATIVE OF A PREDETERMINED BUOYANCY FACTOR FOR THE CORRESPONDING SECTION AND OF A SECOND COMPONENT OUTPUT SIGNAL THAT IS PROPORTIONAL TO A SECOND INPUT SIGNAL APPLIED TO THE SECOND INPUT CHANNEL WITH A GAIN REPRESENTATIVE OF THE PRODUCT OF THE BUOYANCY FACTOR OF THE CORRESPONDING SECTION AND THE DISTANCE OF THE SECTION FROM A FIRST REFERENCE TRANSVERSE PLANE OF THE SHIP, THE FIRST AND SECOND INPUT CHANNELS BEING RESPECTIVELY CONNECTED TO RECEIVE THE DRAUGHT-REPRESENTING AND TRIM-REPRESENTING SIGNALS AS INPUTS, WHEREBY THE TOTAL OUTPUT SIGNAL OF THE BUOYANCY-FORCE-SIGNAL-GENERATING CIRCUIT IS REPRESENTATIVE OF THE BUOYANCY FORCE THAT WOULD BE EXERTED ON THE CORRESPONDING SECTION FOR THE PROPOSED MANNER OF LOADING IF THE SHIP WERE TO HAVE THE VALUES OF DRAUGHT AND TRIM PROVIDED BY THE DRAUGHTREPRESENTING SIGNAL AND TRIM-REPRESENTING SIGNAL GENERATING MEANS, ELEMENTARY SUMMING MEANS CONNECTED TO RECEIVE THE OUTPUTS OF THE WEIGHT-SIGNAL-GENERATING CIRCUIT AND THE BUOYANCY-FORCE-SIGNAL-GENERATING CIRCUIT AS INPUTS AND TO PROVIDE AN OUTPUT SIGNAL THAT IS REPRESENTATIVE IN MAGNITUDE AND SENSE OF THEIR ALGEBRAIC SUM, AND A MOMENT-COMPUTING CIRCUIT OPERATIVE TO PRODUCE AN OUTPUT SIGNAL THAT IS PROPORTIONAL TO AN INPUT SIGNAL WITH AN ADJUSTABLE GAIN, SAID COMPUTER APPARATUS ALSO INCLUDING FIRST AND SECOND PRIMARY SUMMING MEANS, FIRST AND SECOND SWITCH MEANS, SAID FIRST SWITCH MEANS BEING SELECTIVELY OPERABLE TO CONNECT THE OUTPUT SIGNALS OF ALL THE ELEMENTARY SUMMING MEANS TO THE FIRST PRIMARY SUMMING MEANS, AND SAID SECOND SWITCH MEANS BEING SELECTIVELY OPERABLE TO CONNECT ALL THE OUTPUT SIGNALS OF THE ELEMENTARY SUMMING MEANS AS INPUT SIGNALS TO THE CORRESPONDING MOMENT-COMPUTING CIRCUITS, SIMULTANEOUSLY TO ADJUST THE GAINS OF THE MOMENT-COMPUTING CIRCUITS SO AS TO MAKE THE GAINS RESPECTIVELY PROPORTIONAL TO THE DISTANCES OF THE CORRESPONDING SECTIONS FROM A SECOND REFERENCE TRANSVERSE PLANE, AND TO CONNECT THE OUTPUT SIGNALS OF ALL THE MOMENT-COMPUTING CIRCUITS TO SAID SECOND PRIMARY SUMMING MEANS, WHEREBY, BY SUITABLE ADJUSTMENT OF THE DRAUGHT-REPRESENTING-SIGNAL-GENERATING MEANS THE TRIM-REPRESENTING-SIGNAL-GENERATING MEANS TO MAKE THE OUTPUTS OF THE FIRST AND SECOND PRIMARY SUMMING MEANS SUBSTANTIALLY ZERO, MORE ACCURATE VALUES OF DRAUGHT-REPRESENTING AND TRIM-REPRESENTING SIGNALS ARE OBTAINED, SAID SECOND SWITCH MEANS BEING FURTHER SELECTIVELY OPERABLE TO CONNECT THE OUTPUT SIGNALS OF THE ELEMENTARY SUMMING MEANS OF THOSE ELEMENTARY COMPUTING MEANS CORRESPONDING TO THOSE SECTIONS TO ONE SIDE OF THE FIRST PREDETERMINED PLANE AT WHICH IT IS DESIRED TO CALCULATE BENDING MOMENT AS INPUT SIGNALS TO CORRESPONDING MOMENT-COMPUTING CIRCUITS, SIMULTANEOUSLY TO ADJUST THE GAINS OF THE SAID MOMENT-COMPUTING CIRCUITS SO AS TO MAKE THE GAINS RESPECTIVELY PROPORTIONAL TO THE DISTANCES OF THE CORRESPONDING SECTIONS FROM THE SAID FIRST PREDETERMINED TRANSVERSE PLANE, AND TO CONNECT THE OUTPUT SIGNALS OF THE SELECTED MOMENT-COMPUTING CIRCUITS TO THE SECOND SUMMING MEANS TO PROVIDE A MEASURE OF THE BENDING MOMENT. 